Dimming element with edge-mounted illuminators for an optical assembly

ABSTRACT

An optical assembly is configured to receive visible scene light at the backside of the optical assembly and to direct the visible scene light on an optical path toward the eyeward side. The optical assembly includes a dimming element disposed on the optical path, wherein the dimming element includes a photochromic material that is configured to darken in response to exposure to a range of light wavelengths. An illuminator, coupled to an edge of the dimming element, is configured to selectively emit an activation light within the range of light wavelengths to activate a darkening of the photochromic material to dim the visible scene light.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. provisional Application No. 63/284,410 filed Nov. 30, 2021, which is hereby incorporated by reference.

TECHNICAL FIELD

Aspects of the present disclosure relate generally to head mounted devices, and in particular but not exclusively, relate to the dimming of a photochromic material included in an optical assembly of the head mounted device.

BACKGROUND INFORMATION

A smart device is an electronic device that typically communicates with other devices or networks. In some situations the smart device may be configured to operate interactively with a user. A smart device may be designed to support a variety of form factors, such as a head mounted device, a head mounted display (HMD), or a smart display, just to name a few.

Smart devices may include one or more electronic components for use in a variety of applications, such as gaming, aviation, engineering, medicine, entertainment, video/audio chat, activity tracking, and so on. In some examples, a smart device, such as a head-mounted device or HMD, may include a display that can present data, information, images, or other virtual graphics while simultaneously allowing the user to view the real world.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.

FIGS. 1A, 1B, and 1C illustrate a user's view through a near-eye optical assembly of a head-mounted device, in accordance with aspects of the disclosure.

FIG. 2 illustrates a head-mounted device, in accordance with aspects of the disclosure.

FIG. 3A illustrates a dimming element in an undimmed state, in accordance with aspects of the disclosure.

FIG. 3B illustrates the dimming element of FIG. 3A in a dimmed state, in accordance with aspects of the disclosure.

FIG. 4A illustrates another dimming element in an undimmed state, in accordance with aspects of the disclosure.

FIG. 4B illustrates the dimming element of FIG. 4A in a dimmed state, in accordance with aspects of the disclosure.

FIG. 5A illustrates a dimming element with multiple edge-mounted illuminators arranged for global dimming, in accordance with aspects of the disclosure.

FIG. 5B illustrates the dimming element of FIG. 5A in a dimmed state, in accordance with aspects of the disclosure.

FIG. 6 illustrates a dimming element having a reflective coating for containing activation light, in accordance with aspects of the disclosure

FIG. 7 illustrates a portion of a head-mounted device that includes a frame and a dimming element, in accordance with aspects of the disclosure.

FIG. 8 illustrates a dimming element with multiple edge-mounted illuminators arranged for regional dimming, in accordance with aspects of the disclosure.

FIG. 9 illustrates an example computing device for the dynamic control of edge-mounted illuminators, in accordance with aspects of the present disclosure.

DETAILED DESCRIPTION

Embodiments of an apparatus and method for controlling transmission attenuation in augmented reality are described herein. In the following description, numerous specific details are set forth to provide a thorough understanding of the embodiments. One skilled in the relevant art will recognize, however, that the techniques described herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring certain aspects.

Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

In some implementations of the disclosure, the term “near-eye” may be defined as including an element that is configured to be placed within 50 mm of an eye of a user while a near-eye device is being utilized. Therefore, a “near-eye optical element” or a “near-eye system” would include one or more elements configured to be placed within 50 mm of the eye of the user.

In aspects of this disclosure, visible light may be defined as having a wavelength range of approximately 380 nm-700 nm. Non-visible light may be defined as light having wavelengths that are outside the visible light range, such as ultraviolet light and infrared light. Infrared light having a wavelength range of approximately 700 nm-1 mm includes near-infrared light. In aspects of this disclosure, near-infrared light may be defined as having a wavelength range of approximately 700 nm-1.4 μm. Violet light may include light having a wavelength in the range of approximately 380-450 nm.

As mentioned above, a head-mounted device may include a display that is configured to present data, information, images, or other virtual graphics while simultaneously allowing the user to view the real world. However, the virtual graphics may be difficult for the user to view if the environment is too bright, if there is insufficient contrast between the virtual graphics and the user's current view of the real world, if a color of the virtual graphic matches the color of the real world behind the virtual graphic, or some combination thereof. By way of example, FIG. 1A illustrates a user's view of a real-world scene 100 through an optical assembly 102 of a head-mounted device. As shown in FIG. 1A, the optical assembly 102 allows the user to view the real-world scene 100 while simultaneously presenting a virtual graphic 104 to the user. In the illustrated example, virtual graphic 104 is an icon, but in other examples, the virtual graphic 104 may include text, a picture, video, or other visual information that is generated by the optical assembly 102 for presentation to the user. However, as shown in FIG. 1A the virtual graphic 104 is positioned on the optical assembly 102 at the same location as the user's view of a real-world object 106 (e.g., illustrated as a shrub/bush in FIG. 1A). In some examples, the real-world object 106 may interfere with the user's visibility of the virtual graphic 104. That is, the real-world object 106 may be the same or similar color as the virtual graphic 104, and/or the contrast between the real-world object 106 and the virtual graphic 104 may be too low. Thus, in some conditions, the virtual graphic 104 may be difficult for the user to discern when it is co-located with the user's view of the real-world object 106.

Accordingly, aspects of the present disclosure provide for the dimming of light received from the real-world scene 100 to increase the visibility of the virtual graphic 104. For example, FIG. 1B illustrates the darkening of an entire field of view that is provided by the optical assembly 102. In some examples, dimming the entire field of view may be referred to as global dimming. As shown, the dimming provided by the optical assembly 102 reduces or occludes light received from the real-world scene 100 but does not occlude or dim the display light used to generate the virtual graphic 104. Thus, while FIG. 1B illustrates the virtual graphic 104 as being unchanged with respect to the view shown in FIG. 1A, the virtual graphic 104 may have increased visibility due to the darkening of the real-world object 106 provided by the global dimming of the optical assembly 102.

FIG. 1C illustrates an example of optical assembly 102 darkening a region 108, where region 108 is less than the entire field of view provided by the optical assembly 102. In some examples, dimming only a portion of the field-of-view provided by the optical assembly 102 (e.g., less than the entire field-of-view) is referred to as local dimming.

The dimming provided by the optical assembly 102, as shown in FIGS. 1B and 1C, may be provided by a dimming element included in the optical assembly 102. The dimming element may include a photochromic material that darkens in response to exposure to a range of light wavelengths. In some aspects, when activated, the photochromic material may undergo a reversible photochemical reaction that results in a change in its visible light absorption, in strength and/or wavelength.

In some embodiments, the darkening of the dimming element is activated by way of one or more illuminators that are coupled to an edge of the dimming element within the optical assembly 102. The illuminators are configured to selectively emit an activation light to activate the darkening of the photochromic material. These and other aspects will be discussed in more detail below.

FIG. 2 illustrates an example head-mounted device 200, in accordance with aspects of the present disclosure. A head-mounted device, such as head-mounted device 200, is one type of smart device, typically worn on the head of a user to provide artificial reality content to a user. Artificial reality is a form of reality that has been adjusted in some manner before presentation to the user, which may include, e.g., virtual reality (VR), augmented reality (AR), mixed reality (MR), hybrid reality, or some combination and/or derivative thereof.

The illustrated example of head-mounted device 200 is shown as including a frame 202, temple arms 204A and 204B, and a near-eye optical assembly 206A and a near-eye optical assembly 206B. FIG. 2 also illustrates an exploded view of an example of near-eye optical assembly 206A. Near-eye optical assembly 206A is shown as including a display layer 210 and a dimming element 212.

As shown in FIG. 2 , frame 202 is coupled to temple arms 204A and 204B for securing the head-mounted device 200 to the head of a user. Example head-mounted device 200 may also include supporting hardware incorporated into the frame 202 and/or temple arms 204A and 204B. The hardware of head-mounted device 200 may include any of processing logic, wired and/or wireless data interfaces for sending and receiving data, graphic processors, and one or more memories for storing data and computer-executable instructions. In one example, head-mounted device 200 may be configured to receive wired power and/or may be configured to be powered by one or more batteries. In addition, head-mounted device 200 may be configured to receive wired and/or wireless data including video data.

FIG. 2 illustrates near-eye optical assemblies 206A and 206B that are configured to be mounted to the frame 202. The frame 202 may house the near-eye optical assemblies 206A and 206B by surrounding at least a portion of a periphery of the near-eye optical assemblies 206A and 206B. The near-eye optical assembly 206A is configured to receive visible scene light 222 at a backside 211 of the near-eye optical assembly 206A and to direct the visible scene light 222 on an optical path towards the eyeward side 209. In some examples, near-eye optical assembly 206A may appear transparent to the user to facilitate augmented reality or mixed reality such that the user can view visible scene light 222 from the environment while also receiving display light 224 directed to their eye(s) by way of display layer 210. In further examples, some or all of the near-eye optical assemblies 206A and 206B may be incorporated into a virtual reality headset where the transparent nature of the near-eye optical assemblies 206A and 206B allows the user to view an electronic display (e.g., a liquid crystal display (LCD), an organic light emitting diode (OLED) display, a micro-LED display, etc.) incorporated in the virtual reality headset.

As shown in FIG. 2 , the display layer 210 is disposed on the optical path of the near-eye optical assembly 206A, between the eyeward side 209 and the backside 211 of the near-eye optical assembly 206A. In particular, the display layer 210 is disposed between the eyeward side 209 and the dimming element 212. In some examples, display layer 210 may include a waveguide 216 that is configured to direct display light 224 to present one or more virtual graphics to an eye of a user of head-mounted device 200. In some aspects, waveguide 216 is configured to direct display light 224 that is generated by an electronic display to the eye of the user. In some implementations, at least a portion of the electronic display is included in the frame 202 of the head-mounted device 200. The electronic display may include an LCD, an organic light emitting diode (OLED) display, micro-LED display, pico-projector, or liquid crystal on silicon (LCOS) display for generating the display light 224.

FIG. 2 illustrates the dimming element 212 as being disposed on the optical path of the near-eye optical assembly 206A, between the eyeward side 209 and the backside 211. In particular, the dimming element 212 is shown as being disposed between the display layer 210 and the backside 211. In some examples, the dimming element 212 includes a photochromic material that is configured to darken in response to exposure to a range of light wavelengths. For example, the photochromic material may be configured to undergo a reversible photochemical reaction in response to exposure to non-visible light, such as infrared (IR) and/or ultraviolet (UV) light. In other examples, the photochromic material may be activated to darken in response to exposure to violet light having wavelengths in the range of 400 to 440 nm. In some aspects, the photochromic material is a film or dye that is applied to a transparent material, such as a plastic or glass lens. In other aspects, the photochromic material is provided by a photochromic compound that is suspended within a transparent substrate, such as a plastic or glass lens.

In some aspects, the photochromic material of the dimming element 212 is distributed across the entire field-of-view provided by the near-eye optical assembly 206A (e.g., across the entire dimming element 212). In other aspects, the photochromic material may be provided in only certain portions of the field-of-view (e.g., upper half of the dimming element 212).

FIG. 2 also shows the dimming element 212 as including one or more illuminators 214 that are coupled to an edge 213 (i.e., periphery) of the dimming element 212. The illuminator 214 is configured to selectively emit an activation light 226 to activate a darkening of the photochromic material included in the dimming element 212. In some examples, the activation light 226 is within the range of light wavelengths that activate the photochromic material of the dimming element 212 (e.g., IR light, UV light, violet light, etc.).

In some aspects the illuminator 214 may be a light source that generates the activation light 226, such as a light emitting diode, a micro light emitting diode (micro-LED), an edge emitting LED, a vertical cavity surface emitting laser (VCSEL) diode, or a Superluminescent diode (SLED).

In some examples, the dimming element 212 may have a curvature for focusing light (e.g., scene light 222) to the eye of the user. Thus, the dimming element 212 may, in some examples, may be referred to as a lens. In some aspects, the dimming element 212 may have a thickness and/or curvature that corresponds to the specifications of a user. In other words, the dimming element 212 may be a prescription lens.

As mentioned above, the illuminator 214 of the dimming element 212 is configured to emit the activation light 226 to within the dimming element 212 to activate a darkening of the photochromic material. In some examples, enabling of the illuminator 214 is dynamically determined by a computing device of the head-mounted device 200. For instance, the head-mounted device 200 may include a computing device that determines whether the visible scene light 222 will interfere with the visibility of a virtual graphic generated by the visible display light 224. The computing device may make such a determination based on a comparison of a color of the visible scene light 222 and/or by determining a contrast between the visible scene light 222 and the visible display light 224. If the color of the visible scene light 222 is the same or similar to the color of the visible display light 224, and/or if the contrast between the visible scene light 222 and the visible display light 224 is lower than a low-contrast threshold, then the computing device may enable the illuminator 214 to emit the activation light 226 to darken the photochromic material of dimming element 212.

In some aspects, the photochemical reaction of the dimming element 212 that is induced by the activation light 226 may be reversible. In one embodiment, disabling the illuminator 214, such that it no longer emits the activation light 226, allows the photochromic material of the dimming element 212 to naturally revert to its previous non-darkened state. In other embodiments, the head-mounted device 200 may be configured to actively restore the dimming element 212 to its non-darkened state (undimmed) by directing a bleaching light to the dimming element 212. In some examples, the bleaching light may be emitted by the illuminator 214 or by other light sources (not explicitly shown) that are included in the head-mounted device 200. The bleaching light may be light having a wavelength that increases the rate at which the photochromic material is restored to its non-darkened state, such as visible light, UV light, and/or IR light.

FIG. 3A illustrates a dimming element 302 in an undimmed state (un-darkened), whereas FIG. 3B illustrates the dimming element 302 is a dimmed state (darkened), in accordance with aspects of the disclosure. Dimming element 302 is one possible implementation of dimming element 212 of FIG. 2 . Dimming element 302 is shown as including a lens 304, at least one illuminator 306, and a coating 308. As shown in FIG. 3A, illuminators 306 are coupled to an edge 305 corresponding to a periphery of the lens 304, whereas coating 308 is disposed on an optical surface 307 of the lens 304. In some aspects, the coating 308 is a coating of photochromic material that is applied to the optical surface 307. As discussed above, the illuminators 306 may be a light source that is configured to generate activation light 226. As shown in FIG. 3B, the lens 304 is configured to guide the activation light 226 by total internal reflection (TIR). In some implementations the activation light 226 undergoes multiple rounds of total internal reflection inside the lens 304. These multiple bounces may trigger the photochromic material of coating 308 to darken. In some examples, the wavelength of the activation light matches a peak of the photochromic material's absorption spectra.

FIG. 4A illustrates a dimming element 402 in an undimmed state (un-darkened), whereas FIG. 4B illustrates the dimming element 402 is a dimmed state (darkened), in accordance with aspects of the disclosure. Dimming element 402 is one possible implementation of dimming element 212 of FIG. 2 . Dimming element 402 is shown as including a lens 404, at least one illuminator 306, and a dye 406. As shown in FIG. 4A, illuminators 306 are coupled to the edge 405 corresponding to a periphery of the lens 404, whereas dye 406 is embedded within the lens 404. In some aspects, the dye 406 includes photochromic material that is distributed within the lens 404, such as during molding or casting. As discussed above, the illuminators 306 may be a light source that is configured to generate activation light 226. As shown in FIG. 3B, the lens 404 is configured to guide the activation light 226 by total internal reflection (TIR). In some implementations the activation light 226 undergoes multiple rounds of total internal reflection inside the lens 404. These multiple bounces may trigger the photochromic material of dye 406 to darken.

FIG. 5A illustrates a dimming element 500 with edge-mounted illuminators 502, 504, 506, and 508 arranged for global dimming, in accordance with aspects of the disclosure. Dimming element 500 is one possible implementation of dimming element 212 of FIG. 2 . As shown in FIG. 5A, illuminators 502-508 are mounted on a periphery edge 505 of the dimming element 500. Although FIG. 5A illustrates dimming element 500 as including four illuminators 502-508, any number of illuminators may be provided by the dimming element 500, including one or more. In some instances, the illuminators 502-508 are positioned on the edge 505 to direct activation light into the dimming element 500 to achieve global dimming (i.e., across the field of view). By way of example, FIG. 5B illustrates the global dimming of dimming element 500 provided by illuminators 502-508 emitting activation light 226. In some implementations, the activation light 226 propagates through the dimming element (by way of TIR) but may eventually leak out through the edge 505. Thus, in some examples, the intensity of the activation light 226 that is generated by the illuminators 502-508 is set to be greater that an activation threshold needed for the photochromic material to darken. In other examples, a reflective coating may be included on the edges of the dimming element to reduce or prevent leakage of the activation light 226. By of example, FIG. 6 illustrates a dimming element 600 having a reflective coating 602 for containing activation light 226, in accordance with aspects of the disclosure. As shown in FIG. 6 , the reflective coating 602 is disposed on an edge 605 (i.e., periphery) of the dimming element 600 and may be configured to reflect activation light 226 within the dimming element 600. In some examples, the reflective coating 602 is minimally transmissive to the range of wavelengths corresponding to the activation light 226.

Although the reflective coating 602 may be minimally transmissive to the activation light 226, in operation, some activation light 226 may continue to leak, primarily at the locations corresponding to the illuminators 502-508, themselves. Accordingly, in some examples, the frame in which the optical assembly is to be placed may be configured to absorb or block activation light 226 that continues to escape the dimming element. For example, FIG. 7 illustrates a portion 700 of a head-mounted device that includes a frame 702 and dimming element 600, in accordance with aspects of the disclosure. As shown, the frame 702 may be configured to completely encompass or cap the dimming element 600 at its periphery to block or absorb any leaking activation light 226.

FIG. 8 illustrates a dimming element 800 with multiple edge-mounted illuminators 802 and 804 arranged for regional dimming, in accordance with aspects of the disclosure. Dimming element 800 is one possible implementation of dimming element 212 of FIG. 2 . As shown in FIG. 8 , illuminators 802-804 are mounted on a periphery edge of the dimming element 800. Although FIG. 800 illustrates dimming element 800 as including two illuminators 802-804, any number of illuminators may be provided by the dimming element 800, including one or more. In some instances, the illuminators 802-804 are positioned on the edge of dimming element 800 to direct activation light into the dimming element 800 to achieve regional dimming (i.e., less than the entire field of view). By way of example, FIG. 8 illustrates the regional dimming of dimming element 800 provided by illuminators 802-804 emitting activation light 226 to darken region 806.

FIG. 9 illustrates an example computing device 902 for the dynamic control of edge-mounted illuminators, in accordance with aspects of the present disclosure. The illustrated example of computing device 902 is shown as including a communication interface 904, one or more processors 906, hardware 908, and a memory 910. In one example, one or more of the components illustrated in FIG. 9 may be incorporated into the frame 202 and/or temple arms 204A/204B of the head-mounted device 200 of FIG. 2 . In other examples, one of more of the components illustrated in FIG. 9 may be incorporated into a remote computing device that is communicatively coupled to the head-mounted device 200 for performing one or more aspects of the dynamic control of the illuminators.

The communication interface 904 may include wireless and/or wired communication components that enable the computing device 902 to transmit data to and receive data from other networked devices. The hardware 908 may include additional hardware interface, data communication, or data storage hardware. For example, the hardware interfaces may include a data output device (e.g., electronic display, audio speakers), and one or more data input devices.

The memory 910 may be implemented using computer-readable media, such as computer storage media. In some aspects, computer-readable media may include volatile and/or non-volatile, removable and/or non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules, or other data. Computer-readable media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD), high-definition multimedia/data storage disks, or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transmission medium that can be used to store information for access by a computing device.

The processors 906 and the memory 910 of the computing device 902 may implement a display module 912 and a dimming control module 914. The display module 912 and the dimming control module 914 may include routines, program instructions, objects, and/or data structures that perform particular tasks or implement particular abstract data types. The memory 910 may also include a data store (not shown) that is used by the display module 912 and/or dimming control module 914.

The display module 912 may be configured to determine that the visible scene light (e.g., visible scene light 222 of FIG. 2 ) of the near-eye optical assembly will interfere with a visibility of a virtual graphic (e.g., virtual graphic 104 of FIG. 1 ) that is generated by the visible display light 224. In some implementations, the head-mounted device may include one or more light sensors that provide information about the visible scene light (e.g., brightness, contrast, color, etc.). In another implementation, the head-mounted device may include a camera that is positioned (e.g., on the temple arm 204B of FIG. 2 ) to obtain images of the field-of-view provided by the optical assembly. The display module 912 may receive the images and/or data from the light sensor to determine whether the visible scene light is interfering with a visibility of the virtual graphic.

In some aspects, the display module 912 determines the visibility of the virtual graphic based on readings obtained from the light sensors and/or by performing image processing on images of the field-of-view. This may include determining an ambient brightness and/or determining a contrast between the visible scene light and the virtual graphic. In another example, the display module 912 may determine the visibility of the virtual graphic by comparing a color of the visible scene light in a region that corresponds to where the virtual graphic is to be displayed. If the visible scene light is too bright, the contrast between the scene light and the virtual graphic is too low, and/or if a color of the scene light is similar to that of the virtual graphic, then the display module 912 then determines that the visible scene light will indeed interfere with the visibility of the virtual graphic.

In response the determination by the display module 912 that the visible scene light will interfere with the visibility of the virtual graphic, the dimming control module 914 may then activate the darkening of one or more regions of the dimming element of the near-eye optical assembly to dim and/or occlude the visible scene light. For example, with reference to head-mounted device 200 of FIG. 2 , the dimming control module 914 may enable illuminator 214 to emit the activation light 226 to activate the darkening of dimming element 212. As discussed above, the darkening of the dimming element 212 may dim the visible scene light 222 to increase the visibility of the virtual graphic generated by display light 224.

Embodiments of the invention may include or be implemented in conjunction with an artificial reality system. Artificial reality is a form of reality that has been adjusted in some manner before presentation to a user, which may include, e.g., a virtual reality (VR), an augmented reality (AR), a mixed reality (MR), a hybrid reality, or some combination and/or derivatives thereof. Artificial reality content may include completely generated content or generated content combined with captured (e.g., real-world) content. The artificial reality content may include video, audio, haptic feedback, or some combination thereof, and any of which may be presented in a single channel or in multiple channels (such as stereo video that produces a three-dimensional effect to the viewer). Additionally, in some embodiments, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof, that are used to, e.g., create content in an artificial reality and/or are otherwise used in (e.g., perform activities in) an artificial reality. The artificial reality system that provides the artificial reality content may be implemented on various platforms, including a head-mounted display (HMD) connected to a host computer system, a standalone HMD, a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers.

The above description of illustrated embodiments of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.

These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation. 

What is claimed is:
 1. An optical assembly, comprising: an eyeward side and a backside, wherein the optical assembly is configured to receive visible scene light at the backside of the optical assembly and to direct the visible scene light on an optical path toward the eyeward side; a dimming element disposed on the optical path between the eyeward side and the backside, wherein the dimming element includes a photochromic material that is configured to darken in response to exposure to a range of light wavelengths; and at least one illuminator coupled to an edge of the dimming element, wherein the at least one illuminator is configured to selectively emit an activation light within the range of light wavelengths to activate a darkening of the photochromic material to dim the visible scene light.
 2. The optical assembly of claim 1, wherein the dimming element comprises a lens, and wherein the photochromic material is included in a coating on at least one optical surface of the lens.
 3. The optical assembly of claim 1, wherein the dimming element comprises a lens, and wherein the photochromic material is included in a dye embedded within the lens.
 4. The optical assembly of claim 1, wherein the dimming element is configured to guide the activation light by total internal reflection to activate the darkening of the photochromic material.
 5. The optical assembly of claim 4, wherein the at least on illuminator is configured to selectively emit the activation light to darken the photochromic material across a field of view provided by the optical assembly.
 6. The optical assembly of claim 5, further comprising a reflective coating disposed on the edge of the dimming element, wherein the reflective coating is configured to reflect the activation light within the dimming element.
 7. The optical assembly of claim 1, wherein the at least one illuminator is configured to selectively emit the activation light to darken the photochromic material for a region that is less than a field of view provided by the optical assembly.
 8. The optical assembly of claim 1, wherein the activation light comprises non-visible light, ultraviolet light, infrared light, or violet light.
 9. The optical assembly of claim 1, further comprising: a display layer disposed on the optical path between the eyeward side of the optical assembly and the dimming element, wherein the display layer is configured to direct visible display light toward the eyeward side.
 10. A head-mounted device, comprising: a frame; and an optical assembly secured within the frame, wherein the optical assembly is configured to receive visible scene light at a backside of the optical assembly and to direct the visible scene light on an optical path toward an eyeward side of the optical assembly, wherein the optical assembly includes: a dimming element disposed on the optical path between the eyeward side and the backside, wherein the dimming element includes a photochromic material that is configured to darken in response to exposure to a range of light wavelengths; and at least one illuminator coupled to an edge of the dimming element, wherein the at least one illuminator is configured to selectively emit an activation light within the range of light wavelengths to activate a darkening of the photochromic material to dim the visible scene light.
 11. The head-mounted device of claim 10, wherein the dimming element is configured to guide the activation light by total internal reflection to activate the darkening of the photochromic material.
 12. The head-mounted device of claim 11, wherein the at least one illuminator is configured to selectively emit the activation light to darken the photochromic material across a field of view provided by the optical assembly.
 13. The head-mounted device of claim 12, further comprising a reflective coating disposed on the edge of the dimming element, wherein the reflective coating is configured to reflect the activation light within the dimming element.
 14. The head-mounted device of claim 13, wherein the frame positioned to absorb activation light that escapes the dimming element through the at least one illuminator at the edge of the dimming element.
 15. The head-mounted device of claim 10, further comprising: a computing device included in the frame and configured to control the at least one illuminator to emit the activation light.
 16. The head-mounted device of claim 10, wherein the activation light comprises non-visible light, ultraviolet light, infrared light, or violet light.
 17. The head-mounted device of claim 10, wherein the optical assembly further comprises: a display layer disposed on the optical path between the eyeward side of the optical assembly and the dimming element, wherein the display layer is configured to direct visible display light toward the eyeward side.
 18. An optical assembly, comprising: a dimming element that includes: a lens; and a photochromic material, wherein the photochromic material is included in a coating on an optical surface of the lens or in a dye embedded within the lens, wherein the photochromic material is configured to darken in response to exposure to a range of light wavelengths; and a plurality of illuminators coupled to an edge of the lens, wherein the plurality of illuminators are configured to selectively emit an activation light within the range of light wavelengths to activate a darkening of the photochromic material to dim visible scene light, and wherein the dimming element is configured to guide the activation light by total internal reflection.
 19. The optical assembly of claim 18, wherein the dimming element further comprises a reflective coating disposed on the edge of the dimming element, wherein the reflective coating is configured to reflect the activation light within the dimming element.
 20. The optical assembly of claim 18, wherein the activation light comprises non-visible light, ultraviolet light, infrared light, or violet light. 